while True:
    #输入用户名和密码
    username = input("请输入用户名和密码：")
    if username == "exit":
        print("退出")
        break
    password = input("请输入密码：")
    if (username == "admin") and (password == "123456"):
        print("登录成功！")
        break
    else:
        print("用户名或密码错误，请重修输入")
        